Method of filtering tobacco smoke



United States Patent 3,461,882 METHOD OF FILTERING TOBACCO SMOKE Martin E. Epstein, Charlotte, N.C., and Saunders E. Jamison, Summit, N.J., assignors to Celanese Corporation, New York, N.Y., a corporation of Delaware N0 Drawing. Filed May 8, 1967, Ser. No. 636,632 Int. Cl. B01d 35/06; A24f 7/04, 25/00 US Cl. 131-262 1.Claim ABSTRACT OF THE DISCLOSURE A method of filtering tobacco smoke is described in which a filter is interposed in the smoke stream which comprises two fibers.

DISCLOSURE This invention relates in general to smoke filters, and more specifically to the method of filtering tobacco smoke employing filters exhibiting improved smoke removal efficiency.

At the present time, various materials are employed as filtration media for the removal of tars, nicotine and other undesirable constituents from cigarette smoke. Such materials include cellulose acetate fibers, cellulose paper, cotton, asbestos, and more recently, polyolefin fibers.

In addition to filters formed from the foregoing materials, more complex filters have been previously suggested. In the brief review of the patent art which follows, suggestions relating somewhat to the present invention, but clearly distinguishable therefrom, will be discussed.

United States Patent No. 2,979,433 to MacHenry discloses mixing and aligning rayon and vinyon fibers in the initial stages of filter formation, followed by a heating stage, wherein the vinyon fiber is melted to form bonding points between the rayon fibers.

Similarly, United States Patent No. 3,229,008 to Harrington, Jr., et 211. discloses mixing of polyethylene and polypropylene fibers and then heating the mixed fibers to melt the polyethylene which forms bonding points between the polypropylene fibers.

United States Patent No. 2,805,671 to Hackney et al. discloses a filter comprising a group of fibers aligned parallel to the smoke flow, with microscopic fibers (not exceeding 1000 microns) adhered perpendicularly there to. Consequently, said microscopic fibers which may be the same as or different from the longitudinal fibers are perpendicular to the smoke flow and thus serve to impair passage of undesirable smoke constituents.

While the aforesaid filters have proven to be effective to some extent, there is a continuing search in the industry for new filters which will exhibit improved smoke removal efficiency.

It is, therefore, an object of this invention to provide a new method of filtering tobacco smoke in which an improved filter is interposed in the smoke stream which is effective in removing undesirable constituents from cigarette smoke.

Further objects of the present invention, if not specifically set forth herein, will be readily apparent to one skilled in the art from a reading of the following detailed description.

Generally, the objects of the present invention are attained by the preparation and use of a smoke filter containing at least two different fibers which differ substantially in electron affinity and which are free of induced charge. For the sake of convenience, the following description will be directed to the preparation of filters containing only the two required fibers. However, it will be readily apparent that other fibers and additives may also be present.

Selection of the fibers which differ in the required degree of electron afiinity is facilitated by the triboelectric series. The triboelectric series has been previously described in the prior art, for example, in US. Patent 2,949,134 to Hindle et al.; Lemicke, American Dyestuff Reporter, 38 (1949), 853; and Ballou, Textile Research Journal, 24 (1954), 146.1n essence, the triboelectric series is an arrangement of fibers in descending order from the relatively more electropositive fibers to those fibers which are relatively more electronegative. The series generally 1conforming to the results of prior art workers is as folows:

glaSS paper y n acetate wool triacetate silk polyester viscose acrylic cotton polyolefin The above series may differ slightly from particular prior art results because of the experimental techniques employed. However, these slight variations will not affect the utility of the above series in the selection of fibers suitable for the present invention.

In the preceding series, the term nylon is intended to encompass not only nylon 66, but also other polyamides, such as nylon 6, nylon 610 and nylon 6T.

The term polyolefin in the foregoing series is to be understood as encompassing homopolymers and copolymers of olefins such as ethylene, propylene and butylene. Since these materials are substantially equally positioned in the triboelectric series, mixtures thereof may also be employed.

In addition to the fibers specifically noted in the above series, .it will be obvious to one skilled in the art from a reading of the present disclosure that various other fibers are also applicable in the present invention. Further, conjugate filaments and filaments prepared from polymer blends are also applicable. In using a fiber not specifically shown in the above series, it will only be necessary for the skilled artisan to determine the position of the fiber in the triboelectric series through routine experimentation by utilization of prior art techniques.

In preparing the present filter, two fibers are selected which differ substantially in electron affinity, e.g., fibers on the above chart which are separated by at least one other fiber. The fibers may then be cut into short lengths, e.g. from at least about 1 mm. to about 600 mm., and preferably above about 1.5 mm. and intimately mixed. After mixing, the fibers are formed into a filter structure, e.g. by wrapping in a filter cover paper.

Alternatively, it may be desirable to form the filter from an intimately mixed tow of the different fibers, and then cut the fibers to the required size after filter formation.

Also, it should be understood, that the present process may include additional steps, such as addition of plasticizers and positioning of the fibers in a random, somewhat random, or substantially parallel configuration.

While the ratio of the fibers will vary to some extent depending on the particular fibers selected, as Well as the presence of other materials, a Weight to Weight ratio of generally from about 10:1 to 1:10 is ordinarily effective, with a ratio of about 2:1 to about 1:2 being preferred. While the foregoing ratios are most desirable in the production of the present improvement, it should be realized that ratios without the specified ranges will still produce some improvement, particularly where Widely divergent fibers are employed.

Generally, the fibers employed in the described invention will contain about 5 to 15 crimps per inch, and will be of 1.6 to 16 or more denier. However, operation within the aforesaid crimp and denier levels is not critical to the present invention, which may also be practiced with fibers of other crimp and/or denier.

Formation of the fibers into a filter by the preceding methods yields a filter having fibers in a spaced relationship along a portion of their length. Because of this spaced relationship, a potential difference will be created between the different fibers. Although not wishing to be held to any particular theory, it is believed that it is this potential difference that yields the increased efiiciency in smoke removal. That is, it is believed that impurities, when drawn through spaced portions of the filter as charged particles, tend to be attracted to the electropositive or electronegative fiber, depending upon the charge of the particle. Thus, the particles are retained within the filter.

While the prior art discussed earlier has described the formation of cigarette filters from two different fiber materials, it will be obvious to one skilled in the art upon a reading of the present description, that the above electrostatic effect will not be produced therein because of the failure of these prior art techniques to intimately mix different fibers of sufiicient length in the final filter in the manner presently described.

In the examples which follow, filter rods 17 mm. in length prepared from the designated fiber or fibers were attached to 68 mm. cigarettes and smoked to 30 mm. butts on cigarette smoking machines. A smoking cycle of a 35 cc. puff of two seconds duration, once a minute, was emplo yed. About puffs were normally required in smoking the cigarettes to the above butt length. The smoke drawn through the cigarette was collected on an absolute filter, i.e., a smoke filter pad of sufficiently low porosity to retain all of the particulate matter in the smoke. The increase in the Weight of the pad caused by the smoking of the filter cigarette in relation to the increase caused by the smoking of the unfiltered cigarette then provided a basis for computing the smoke removal efficiency of the cigarette filter. That is, the average percent of smoke removed Was determined by first subtracting the weight of the material collected on the absolute filter upon smoking of a filtered cigarette from the amount collected upon smoking an unfiltered cigarette. This initial calculation gave the amount of material retained by the filter. Then, the percent of smoke removed was obtained by dividing the total amount of material in the smoke, as evidenced by the amount removed by the absolute filter from the smoke of an unfiltered cigarette, into the amount retained by the filter.

It is to be understood that the following examples are presented for the purpose of illustration only and are not to be construed as limiting the scope of the invention.

Example I Cigarette filter rods were prepared from 3 denier 1.5

inch nylon 66 crimped staple fiber, 3 denier 2.0 inch poly- 7 propylene crimped staple fiber, and from a homogeneous 4 blend of equal weights of these fibers. The fibers were first aligned by carding and then wrapped in cigarette paper in a cylinder of 8 mm. diameter. Smoking of the cigarettes according to the above procedure yielded the following results:

TABLE 1.-SMOKE FILTRATION EFFICIENCY OF CIGA- RETTE FILTERS MADE FROM NYLON 66 AND POLY- PROPYLENE FIBERS AND A MIXTURE OF THE TWO In a second experiment under conditions similar to those of Example I, it was determined that a cellulose acetate filter having a pressure drop of 51.7 mm. Hg gave a percent smoke removal efficiency (percent S.R.E.) of 42.0, while a filter of a 25%/ ratio of polypropylene/ cellulose acetate gave a percent S.R.E. of 49.2 at a pres sure drop of 52.4 mm. Hg. Although this percent S.R.E. is less than a 59.3% S.R.E. at a pressure drop of 51.7 mm. Hg. obtained with a polypropylene filter, it is still more than would be expected with such a mixture, illustrating the influence of the electrostatic eifect.

While the present invention has been described with particular reference to cigarette smoke filters, it should be understood that the disclosed improvement is also applicable generally to other filters employed in the purification of smoke which contains charged particles, e.g., industrial and household filters.

We claim:

1. The method of filtering tobacco smoke which com prises providing an intimate mixture of crimped nylon fibers and polyolefin fibers, the said polyolefin being selected from the group consisting of homopolymers, copolymers or mixtures thereof, of ethylene, propylene and butylene, said fibers being at least 1.5 mm. in length, of about 1.6 to 16 denier and having substantially 5-15 crimps per inch, the weight ratio of said fibers being from about 2:1 to about 1:2, said nylon and polyolefin fibers being non adhesively associated in such manner as to manifest a spaced relationship along a portion of their length suflicient to create a potential difference therebetween and effect thereby the attraction to the fibers of charged particles in the smoke stream.

References Cited UNITED STATES PATENTS 2,765,515 10/1956 Knudson 13110.9 X 2,774,680 12/1956 Hackney et al. 13110.9 X 2,796,810 6 1957 Muller.

2,812,767 11/1957 MacHenry 13110.9 2,916,038 12/1959 Wade 13110.9 2,933,154 4/ 1960 Lauterbach.

2,966,157 12/1960 Touey et al. 131-269 3,028,864 4/1962 Minto 131-262 3,144,025 8/1964 Erlich 131--269 X 3,229,008 1/ 1966 Harrington et al. 131-269 X MELVIN D. REIN, Primary Examiner US. Cl. X.R. 131-264, 269 

